Electron discharge device



Ap 1933- w. D. COOLIDGE. 7 2,113,422

ELECTRON DISCHARGE DEVICE I Filed June 12, 1931 IIIIIIIIIIIIII/If;

Inventor: I William D. Coolidge, by MW His Attorney.

Patented Apr. 5, 1938 PATENT OFFICE ELECTRON DISCHARGE DEVICE William D.Coolidge, Schenectady, N. 2., assignor to General Electric Company, acorporation of New York Application June 12, 1931, Serial No. 543,992

18 Claims.

The present invention comprises an improvement in the construction ofelectron devices in which a beam of electrons (otherwise known ascathode rays) is produced. For example, my invention may be utilized incathode ray tubes and X-ray tubes. It is particularly applicable to theconstruction of such devices in which a plurality of discharge membersare operated in cascade, that is, in which the cathode rays are givensuccessive cumulative accelerations in their passage through the tube.Such a device is described in my prior application Serial No. 244,014,filed December 31, 1927 (British Patent 322,662),

The device described in this prior application provides one or moreapertured electrodes located intermediate the main electrodes. Theelectrons in their passage from the main cathode to the main anode passthrough apertures in the intermediate electrodes. It has been founddiflicult to construct such a cascade discharge device with sufiicientaccuracy to cause the cathode ray beam to traverse the discharge spacewithout striking the intermediate electrodes and to some extent beingdischarged thereon. It is desirable to have the cathode ray beam passthrough the device along its axis without being discharged evenpartially upon an intermediate electrode.

In accordance with my present invention, I have provided a constructionwhereby the direction and diameter of a beam of cathode rays may bevaried by changing the position of the parts of the cathode structurewith respect to one another-from the exterior of an operating dischargedevice without disturbing the assembly of parts a or disturbing theevacuated condition of the device. In order to carry out the desiredadjustments, I have provided a cathode construction which by employmentof extensible and compressible members between the parts of the oathodeand the envelope provides for the variation of the spatial relations of.the cathode members so as to produce the desired changes.

The novel features of my invention will be described in greater detailin the accompanying specification taken in connection with theaccompanying drawing in which Fig. 1 is a side elevation of an electrondischarge device embodying my invention; Fig. 2 is a longitudinalsection on a larger scale of the cathode structure; and Fig. 3 is afragmental sectional view of part of the anode.

The device shown in Fig. 1 of the drawing comprises an envelopeconsisting of bulbs l and 2, ordinarily consisting of glass, connectedby a conductive coupling 3. In Fig. 1 of the drawing,

the coupling 3 is shown surrounded by a rounded corona guard. The numberof bulbs is not limited to the number shown herein. The bulb I containsa. cathode structure 4 (to be hereinafter more fully described) fromwhich a beam of electrons, or "cathode rays is projected through atubular intermediate electrode 5 which is mounted upon and electricallyconnected to the coupling 3. The electrode 5 extends from the bulb iinto the bulb 2 of the envelope, the righte hand part of the electrode 5being of greater diameter than the left-hand part. The cathode beamemerging from the tubular electrode 5 enters a second tubular electrode6 which is joined to an anode member I by a coupling 8. The anode l, asshown in Fig. 3, comprises a hollow metal tube consisting of brass, orother suitable metal. To the inner surface of the closed outer end ofthe anode (see Fig. 3) is attached a thin plate 9 of tungsten on theback of which has been cast a layer of copper, preferably in a vacuum.To this layer of copper is attached a brass cell provided with passagesII! for the circulation of water, or other cooling fluid. The connectionbetween these passages and the supply tubes for the cooling fluid arenot shown to avoid complication of the drawing. Inlet and outlet tubesfor the cooling fluid are indicated externally at H, in Fig. 1.Surrounding the tubular electrode 6 is a magnetic coil I2, whereby thecathode beam may be focussed. This coil is supported by brackets 13 froma wall member through which the anode projects. This wall may be made ofmaterial impervious to X-rays. The coupling 8 is grounded and asindicated is connected to a suitable vacuum system through a tube I 4.

As shown in Fig. 2, the cathode structure 4 of Fig. 1 comprises afilament l5 which is surrounded by a hollow molybdenum cylinder and isconnected to the current-conveying conductors l6, l5. Surrounding thefilament I5 is a toroidshaped focussing member ll, which may be made ofcopper having rounded surfaces to reduce cold cathode effect. Thefilament I5 is located near the bottom of the depressed or dishedportion of the focussing member ll thereby causing the electronsemanating from the filament to be iocussed to form a beam, due to thedistribution of the electrostatic field. This circumscribed beamtraverses the tube passing through the eleco trodes 5 and 6, finallyreaching the anode where either X-rays are produced or where part of thecathode rays pass through the anode to the exterior of the dischargetube, depending on the character of the anode, as well known.

The focussing device I! is mounted upon three rods of which two, 20, 2|,are shown. These rods are connected to the plate It by three extensibleand compressible bellows members, two of which, 22 and 23, are shown.Such bellows members are commonly made of copper and commonly are termedsylphons. As is apparent from the drawing, the rotation of the nut 24upon the threaded end of the rod 20 will shorten or lengthen the portionof the rod 20 intermediate the members I and I8, depending on thedirection of its rotation. The sylphon member 22 will be eithercompressed or extended, thereby tilting the focussing ring or, in otherwords, changingthe position of the focussing member with respect to thetube axis and causing the beam of cathode rays to be correspondinglytilted. When the rod 20 is lengthened to tilt the focussing member I!forward at the top, then the cathode ray beam is moved in a downwarddirection, and conversely pushing forward of the lower portion of themember |1 directs the beam upwardly. The other two rods may be similarlyadjusted. For convenience the rods 20 and 2| are made of severalsections. Surrounding the supporting rods is a large cylindrical metaltube 26, which may be made of brass, and which is joined by screws to abase plate 21 to which the bulb is sealed by cement or otherwise asindicated at 28. It is the function of the tube 26 to shield the cathodesupply wires and other parts within the same from deleterious electricaldischarges during the operation of the device and to support a plate 29provided for guiding and supporting the rods 20 and 2|, as indicated.

My invention also provides means for varying the axial position of thefilament IS with respect to the focussing member I1. In other words, thefilament |5 may be either drawn further into the hole or cavity of thefocussing member or pushed further out.

The cathode supply wires I6, l5 pass through a tube 3| which isconnected by a sylphon 32 to a threaded closure plug 33 for the platel8. The wires l6, l6 are spaced at the end of the tube nearest thefilament |l5 by passing through apertures in an insulating plug 34. Atthe outer or left-hand end of the tube 3|, which projects beyond theplate 18 the wires I6 and I6 pass through and are rigidly held ininsulators 35 and 36, which are embedded in a metal plug 31. This metalplug is connected to the sylphon 32. Upon the plug 31 is mounted a rod38 which projects through a housing 39 for the sylphon member 32. Bymoving the nut 40 upon the threaded portion of the rod 38, the cathodefilament with its, surrounding molybdenum tube can be movedlongitudinally with respect to the focussing member When the cathodefilament I5 is drawn into the passage of the focussing member thefocussing is made sharper, that is, the beam of cathode rays becomesmore circumscribed and conversely when the filament is moved outwardlythe focus of the cathode ray beam is broadened.

Although the electrical circuit connections form no part of my presentinvention, they have been shown for illustrative purposes. Referring toFig.1, the cathode filament I5 is connected by circuit conductors 43,44, to a suitable source of heating current, such as a battery 45 inseries with an adjustable resistance 46 and a switch 41. The maincathode of the tube and the grounded anode are connected by theconductor 48 and the grounded conductors 49, 43' to the high tensionterminals of the secondary of an induction coil 5|]. The middle point ofthe secondary of this coil is connected to the intermediate electrode 5by a conductor 5|. The primary of the coil 50 is connected to thesecondary winding of a transformer 52 in series with an interrupter 53,including a condenser shunting the make and break device. In circuitwith the primary of the transformer 52 is an auto-transformer 54 whichis employed for regulating purposes.

With the proper adjustment of the electrostatic focussing member none ofthe cathode rays strike the intermediate electrodes as may be shown bythe fact when a milliammeter is placed in series with the conductor 5|leading to the electrode 5 it indicates no current while the device isoperating. The focal spot may be brought to the exact position desiredon the target or anode face by slightly tilting the elec- 'trostaticfocussing member IT as above described.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. An electron discharge device comprising the combination of a sealedenvelope constituted in part of an anode, a focussing member and amovable cathode in said envelope, leading-in conductors connected tosaid cathode, said envelope including an extensible member rigidlymounted with respect to said conductors and adapted to move the cathodewith respect to all of the remaining electrodes.

2. An X-ray tube comprising the combination of a sealed evacuatedenvelope, electrodes therein including a cathode, a focussing member anda target, mechanical means operable from the exterior of the envelopefor adjusting the longitudinal position of the focussing member withrespect to said target, said means including a mechanical connection tothe focussing member.

3. An electron discharge device comprising the combination of a sealedevacuated envelope comprising a plurality of sections joined end to end,a cathode located at one extremity of said envelope, an anode located atthe opposite extremity and at least one tubular intermediate electrodethrough which an electrical discharge from said cathode to said anodepasses, said electrode having a length several times greater than thediameter thereof, a focussing member surrounding said cathode, supportsfor said member passing through said envelope to the exterior, andconnections between said supports and said envelope permitting movementof said supports and focussing member relative to the envelope,wherebythe discharge is constrained to a bundle of rays which passesthrough the entire length of said tubular electrode in a focussedcondition.

4. A cathode structure for electric discharge tubes comprising thecombination of a filament,

va focussing member surrounding said filament,

a support for said filament, a compressible and extensible link securedto said support and manually operable mechanical means for changing theposition of said filament with respect to the focussing member throughthe intermediary of said link.

5. An electron discharge device comprising an evacuated envelopecontaining a movable cathode, and a focusing device surrounding thecathode, an anode positioned at the opposite end of the envelope fromsaid cathode, a support for said cathode, said support including acompressible and extensible member which constitutes part of theenvelope, and means'mounted on the exterior of the envelope forcompressing and extending said member whereby the cathode may be movedwith respect to the focusing device.

6. An X-ray tube comprising an evacuated envelope containing a movablefilamentary cathode, and a movable focusing device surrounding thefilament, a stationary anode positioned at the opposite end of theenvelope from said cathode, a support for said focusing device includinga compressible and extensible member, a support for said filamentincluding a compressible and extensible member, both of said membersconstituting part of the envelope, and means mounted on the exterior ofthe envelope for compressing and extending said members whereby thefocusing device and the filament may be moved with respect to oneanother and with respect to the anode.

7. An electron discharge device comprising the combination oi. a sealedevacuated envelope comprising a plurality of sections joined end to end,

an electron-emitting cathode located at one extremity of said envelope,an anode located at the opposite extremity and at least one tubularintermediate electrode through which a discharge from said cathode tosaid anode passes, a focusing member surrounding the cathode forconstraining the electrons to a bundle of rays having a diametral sizeless than the interior diameter of the tubular electrode, and means foradjusting the focusing member with respect to the tubular electrodewhereby the bundle of rays may be caused to pass through said electrodewithout striking.

8. An electron discharge device comprising the combination of a sealedevacuated envelope comprising a plurality of sections joined end to end,a cathode structure located at one extremity of said envelope, an anodelocated at the opposite extremity and at least one tubular intermediateelectrode through which an electrical discharge from said cathode tosaid anode passes, said cathode structure comprising a thermionicelectron emitter, a surrounding focussing member, a supporting structurefor said focussing member and a supporting structure for said electronemitter, said structures passing through the envelope to the exteriorand being separately movable with respect to the envelope whereby thecathode and the focusing member respectively are movable with respect toone another and with respect to the envelope.

9. An electron discharge device comprising an evacuated envelopecontaining a cathode and a focussing device surrounding the cathode, ananode positioned at the opposite end of the envelope from said cathode,a plurality of supports equidistantly spaced about said focussingdevice, said supports including compressible and extensible memberswhich constitute part of the envelope, and means mounted on the exteriorof the envelope for compressing one of said members and extendinganother of said members whereby the focussing device may be tilted withrespect to the axis of the envelope.

10. An electron discharge device comprising an evacuated envelopecontaining a cathode and a focussing member surrounding the cathode, ananode positioned at the opposite end of the envelope from said cathode,a plurality of supports equidistantly spaced about the focussing device,said supports including compressible and extensible members whichconstitute part of the envelope, asupport for said cathode, said supportincluding a compressible and extensible member which constitutes part ofthe envelope, and means mounted on the exterior of the envelope for ex-vtending one of said members which constitutes part of the focussingdevice supports and for compressing another of said members whichconstitutes part of the focussing device supports, and means mounted onthe exterior of the en-' velope for compressing and extending saidmember which constitutes part of the cathode support, whereby thefocussing device may be tilted with respect to the axis of the envelopeand the cathode may be moved with respect to the focussing device.

11. An electron discharge device comprising the combination of a sealedevacuated envelope comprising a plurality of sections joined end to end,an electron-emitting cathode located at one ex tremity of said envelope,an anode located at the opposite extremity, and at least one tubularintermediate electrode through which a discharge from said cathode tosaid anode passes, a focussing member surrounding the cathodefor'constraining the electrons to a bundle of rays having a dlametralsize less than the interior diameter of the tubular electrode, and meansoperable from the exterior of the envelope for adjusting the focussingmember with respect to the tubular electrode whereby the bundle of raysmay be caused to pass through said electrode without striking. Y

12. An electron discharge device comprising an evacuated envelopecontaining a cathode and a focussing member surrounding the cathode, ananode positioned at a remote end of the envelope from the cathode, saidcathode being movable toward and away from said anode, and meansincluding mechanically operated elements extending from the interior tothe exterior of the envelope for selectively adjusting the position ofthe cathode with respect to the anode during operation of the device.

13. An electron discharge device comprising an evacuated envelopecontaining a cathode, an anode and a focussing member surrounding thecathode, said cathode being adjustably movable with respect to saidmember, and means including mechanically operated elements extendingfrom the interior to the exterior of the envelope for moving the cathodewith respect to said focussing member during operation of the device.

14. An electron discharge device comprising an evacuated envelopecontaining a cathode, an anode and a focussing member surrounding thecathode, said cathode being adjustably movable with respect to saidmember, and cathode-adjusting means manually operable from the exteriorof the envlope for moving the cathode with respect to saidfocussing'member during operation of the device, said means including acompressible and extensible link forming part of the envelope.

15. The combination in an X-ray tube of an evacuated envelope having anaperture leading from the exterior to the evacuated interior thereof, aflexible metallic vacuum-tight closure for said aperture, a target, anelectron-emissive cathode in operative relation to said target for theproduction of X-rays, adjustably variable focussing means forconcentrating the stream of electrons from said cathode into a beamimpinging upon said target, and a mechanism operable upon said focussingmeans for adjustably varying the size of the focal spot, said mechanismbeing also operable to direct said beam to each of a plurality of targetareas successively whereby to vary the position of the focal spotthereon,

said mechanism including said closure,'said target, cathode and focusingmeans being disposed within said envelope.

16. In an X-ray tube, a cathode head comprising, in combination, acathode, an adjustably variable focussing device operatively associatedwith saidcathode, a mechanism including links for operating saidfocussing device, a flexible closure element, said mechanism beingconnected with said closure element, and an operating member connectedto and carried by said closure element, said operating member beingaccessible for manipulation fromthe exterior of the tube.

1'7. An X-ray tube comprising, in combination, an evacuated envelopeincluding a stem having apertures leading into the evacuated interiorthereof, a target, a cathode head in operative relation to said targetfor the production of X-rays, said cathode head including anelectron-emissive cathode, flexible metallic diaphragms sealed to saidstemand forming vacuum-tight closures for said apertures, an adjustablyvariable focussing device and mechanism operable through said diaphragmsfor actuating said i'ocussing device to vary the size 01 the focal-spot,said cathode head being supported by said stem, said target and cathodehead being disposed within said envelope.

18. In an adjustable-focus X-ray tube, an evacuated envelope, a target,an electron-emissive cathode, focussing means situated adjacent saidcathode, said cathode and i'ocussing means being relativeLv movable forvarying the area of the focal spot, a focuss-adju'sting mechanismpartly' within said envelope for effecting relative movement betweensaid cathode and tocussing means, said focuss-adjusting mechanismincluding an operating member extending outside the evacuated interiorof said envelope, said operating member being arranged for manipulationby the operator for effecting focal spot adjustments, and means forholding said i'ocuas-adjusting mechanism in any operating position towhich it 20 happens to be adjusted.

WILLIAM D. COOLIDGE.

